A dozen years of N-confusion: From synthesis to supramolecular chemistry

Abstract

The chemistry of N-confused porphyrin (NCP) and its analogs started in 1994. Since then, considerable progress has been made in understanding the unique properties of NCP and its analogs, which confer characteristic reactivity and metal complex formation. The evolved isomers, multiply NCPs, and expanded N-confused derivatives, have opened up new realms of NCP chemistry. Cis-and trans-doubly N-confused porphyrin (N 2 CP) stabilizes higher oxidation states such as Cu III in square-planar fashion in the core. Confused isomers with five or more pyrrole rings can coordinate several cations owing to their larger cavities compared to tetrapyrrolic system. The peripheral nitrogen(s) of NCP and its analogs can serve as hydrogen-bonding donor and acceptor, and metal coordination site as well. For example, NCP forms versatile dimers with the assistance of metal ions. The square-planar divalent metal complexes of C 6 F 5 -substituted NCP act as efficient anion-binding receptors. Furthermore, Cu III complexes of N 2 CP, possessing both N and NH at the periphery, form self-assembled one-dimensional (1D) hydrogen-bonding networks, whose orientations differ in cis (zigzag) and trans (straight) isomers.

Figure Eights, Möbius Bands, and More: Conformation and Aromaticity of Porphyrinoids

“…It is also a prototype of many related systems, including expanded N-confused, [159] multiply N-confused, [159] and X-confused macrocycles. [18,160] Among the most remarkable reactions of 7-H 2 is the ring fusion process, first reported in 1999, [22,161] and subsequently observed in other porphyrinoid systems.…”

Helical Porphyrinoids: Incorporation of Ferrocene Subunits into Macrocyclic Structures

“…Such an anchoring mode, observed in various porphyrin analogues, is known as "N confusion". [30] In particular, N-confused isomers were observed to form spontaneously in the synthesis of porphyrins (à la Rothemund), [49,50] heteroporphyrins, [51,52] and calixpyrroles (à la Baeyer). [53] Alternatively, 12 and 13 can be viewed as binuclear iron(II) complexes with two bridging ligands.…”

“…Such structures, if they possess at least partial conjugation in the oligopyrrole bridge, will belong to the large family of porphyrin analogues that contain carbo-and heterocyclic rings in place of pyrrole. [29][30][31][32][33][34] Scheme 1.…”

Syntheses of Calix[4]Pyrroles by Amberlyst-15 Catalyzed Cyclocondensations of Pyrrole with Selected Ketones

“…Porphyrinogens, bearing hydrogen atoms at meso positions, are key intermediates in biological and chemical synthesis of porphyrins [18,19]. Various attempts have been made for the development of milder methods for the synthesis of porphyrins [20][21][22], N-C isomerization [23,24] and higher homologues of porphyrins [25]. The meso-octamethylcalix [4]pyrrole 3a has been prepared by condensation of pyrrole with acetone in the presence of aqueous hydrochloric acid or methanesulfonic acid in methanol [26,27].…”